Wafer-to-wafer bonding process

Abstract

There is provided method for controlling bonding of a donor substrate to an acceptor substrate, the method comprising: treating a surface of the donor and / or acceptor substrate; and applying a substrate region specific property to the treated surface of the donor and / or acceptor substrate to locally control an evolution of a bonding wave.

Description

WAFER-TO-WAFER BONDING PROCESSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24183125.4 which was filed on June 19, 2024; EP application 24217687.3 which was filed on December 05, 2024 and EP application 25161915.1 which was filed on March 05, 2025 which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to methods and apparatus for applying patterns to substrates, and in particular to a method of bonding semiconductor substrates in a lithographic manufacturing process.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] In order to monitor the lithographic process, parameters of the patterned substrate are measured. Parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate and critical linewidth (CD) of developed photosensitive resist. This measurement may be performed on a product substrate and / or on a dedicated metrology target. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. A fast and non- invasive form of specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. Two main types of scatterometer are known. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function ofwavelength) of the radiation scattered into a particular narrow angular range. Angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.

[0005] Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. The targets used by such scatterometers are relatively large, e.g., 40pm by 40pm, gratings and the measurement beam generates a spot that is smaller than the grating (i.e., the grating is underfilled). In addition to measurement of feature shapes by reconstruction, diffraction-based overlay can be measured using such apparatus, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark-field imaging of the diffraction orders enables overlay measurements on smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279 which documents are hereby incorporated by reference in their entirety. Further developments of the technique have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A 1. These targets can be smaller than the illumination spot and may be surrounded by product structures on a wafer. Multiple gratings can be measured in one image, using a composite grating target. The contents of all these applications are also incorporated herein by reference.

[0006] Process control methods are used in the manufacture of integrated devices to monitor and control the processes of application of a pattern on a substrate or measurement of such a pattern. Such process control techniques are typically performed to obtain corrections for control of the process. Subsequently, it is sometimes required (for certain devices) to bond substrates together. Bonding processes include die-to-die, die-to-wafer and wafer-to-wafer. Wafer-to-wafer bonding, where whole wafers are permanently bonded together prior to dicing, has the potential of providing a high accuracy and high throughput bonding solution.

[0007] It would be desirable to improve process control methods in the manufacture of integrated devices.SUMMARY OF THE INVENTION

[0008] In an aspect, there is provided method for controlling bonding of a donor substrate to an acceptor substrate, the method comprising: treating a surface of the donor and / or acceptor substrate; and applying a substrate region specific property to the treated surface of the donor and / or acceptor substrate to locally control an evolution of a bonding wave.

[0009] Further aspects, features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additionalembodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:Figure 1 depicts a lithographic apparatus together with other apparatuses forming a production facility for semiconductor devices;Figure 2 comprises a schematic diagram of a scatterometer for use in measuring targets;Figure 3 is a flow diagram describing a present method of manufacturing integrated devices which utilizes wafer-to-wafer bonding;Figure 4 depicts a schematic illustration of a self-assembled monolayer structure on a substrate;Figure 5 depicts a schematic illustration of a substrate or wafer in accordance with some embodiments;Figure 6 depicts a schematic illustration of a substrate or wafer in accordance with some embodiments;Figure 7A depicts a schematic illustration of a self-assembled monolayer structure in accordance with some embodiments;Figure 7B depicts a schematic illustration of a self-assembled monolayer structure in accordance with some embodiments;Figure 7C depicts a schematic illustration of a wafer-to-wafer bonding process in accordance with some embodiments;Figure 8A depicts a schematic illustration of a self-assembled monolayer structure in accordance with some embodiments;Figure 8B depicts a schematic illustration of processed substrate in accordance with some embodiments;Figure 8C depicts a schematic illustration of a wafer-to-wafer bonding process in accordance with some embodiments; andFigure 9 depicts a plurality of self-assembled monolayer structures in accordance with some embodiments.Figure 10 depicts a substrate comprising an exemplary bonding wavefront propagation;Figure 11 depicts a substrate comprising an exemplary plasma modified region in accordance with some embodiments;Figure 12 depicts an exemplary process of applying a plasma to a substrate in accordance with some embodiments;Figure 13 depicts a method of determining locations on a surface of a donor and / or acceptor substrate to be modified.Figure 14 depicts a substrate rinsing process in accordance with some embodiments.DETAILED DESCRIPTION OF THE INVENTION

[0011] Before describing embodiments of the invention in detail, it is instructive to present an example environment in which embodiments of the present invention may be implemented.

[0012] Figure 1 at 200 shows a lithographic apparatus LA as part of an industrial production facility implementing a high-volume, lithographic manufacturing process. In the present example, the manufacturing process is adapted for the manufacture of semiconductor products (integrated circuits) on substrates such as semiconductor wafers. The skilled person will appreciate that a wide variety of products can be manufactured by processing different types of substrates in variants of this process. The production of semiconductor products is used purely as an example which has great commercial significance today.

[0013] Within the lithographic apparatus (or “litho tool” 200 for short), a measurement station MEA is shown at 202 and an exposure station EXP is shown at 204. A control unit LACU is shown at 206. In this example, each substrate visits the measurement station and the exposure station to have a pattern applied. In an optical lithographic apparatus, for example, a projection system is used to transfer a product pattern from a patterning device MA onto the substrate using conditioned radiation and a projection system. This is done by forming an image of the pattern in a layer of radiation-sensitive resist material.

[0014] The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. The patterning MA device may be a mask or reticle, which imparts a pattern to a radiation beam transmitted or reflected by the patterning device. Well-known modes of operation include a stepping mode and a scanning mode. As is well known, the projection system may cooperate with support and positioning systems for the substrate and the patterning device in a variety of ways to apply a desired pattern to many target portions across a substrate. Programmable patterning devices may be used instead of reticles having a fixed pattern. The radiation for example may include electromagnetic radiation in the deep ultraviolet (DUV) or extreme ultraviolet (EUV) wavebands. The present disclosure is also applicable to other types of lithographic process, for example imprint lithography and direct writing lithography, for example by electron beam.

[0015] The lithographic apparatus control unit LACU which controls all the movements and measurements of various actuators and sensors to receive substrates W and reticles MA and to implement the patterning operations. LACU also includes signal processing and data processing capacity to implement desired calculations relevant to the operation of the apparatus. In practice,control unit LACU will be realized as a system of many sub-units, each handling the real-time data acquisition, processing and control of a subsystem or component within the apparatus.

[0016] Before the pattern is applied to a substrate at the exposure station EXP, the substrate is processed in at the measurement station MEA so that various preparatory steps may be carried out. The preparatory steps may include mapping the surface height of the substrate using a level sensor and measuring the position of alignment marks on the substrate using an alignment sensor. The alignment marks are arranged nominally in a regular grid pattern. However, due to inaccuracies in creating the marks and also due to deformations of the substrate that occur throughout its processing, the marks deviate from the ideal grid. Consequently, in addition to measuring position and orientation of the substrate, the alignment sensor in practice must measure in detail the positions of many marks across the substrate area, if the apparatus is to print product features at the correct locations with very high accuracy. The apparatus may be of a so-called dual stage type which has two substrate tables, each with a positioning system controlled by the control unit LACU. While one substrate on one substrate table is being exposed at the exposure station EXP, another substrate can be loaded onto the other substrate table at the measurement station MEA so that various preparatory steps may be carried out. The measurement of alignment marks is therefore very time-consuming and the provision of two substrate tables enables a substantial increase in the throughput of the apparatus. If the position sensor IF is not capable of measuring the position of the substrate table while it is at the measurement station as well as at the exposure station, a second position sensor may be provided to enable the positions of the substrate table to be tracked at both stations. Lithographic apparatus LA may for example is of a so-called dual stage type which has two substrate tables and two stations - an exposure station and a measurement station- between which the substrate tables can be exchanged.

[0017] Within the production facility, apparatus 200 forms part of a “litho cell” or “litho cluster” that contains also a coating apparatus 208 for applying photosensitive resist and other coatings to substrates W for patterning by the apparatus 200. At an output side of apparatus 200, a baking apparatus 210 and developing apparatus 212 are provided for developing the exposed pattern into a physical resist pattern. Between all of these apparatuses, substrate handling systems take care of supporting the substrates and transferring them from one piece of apparatus to the next. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via lithographic apparatus control unit LACU. Thus, the different apparatus can be operated to maximize throughput and processing efficiency. Supervisory control system SCS receives recipe information R which provides in great detail a definition of the steps to be performed to create each patterned substrate.

[0018] Once the pattern has been applied and developed in the litho cell, patterned substrates 220 are transferred to other processing apparatuses such as are illustrated at 222, 224, 226. A wide range of processing steps is implemented by various apparatuses in a typical manufacturing facility. For the sake of example, apparatus 222 in this embodiment is an etching station, and apparatus 224 performs apost-etch annealing step. Further physical and / or chemical processing steps are applied in further apparatuses, 226, etc. Numerous types of operation can be required to make a real device, such as deposition of material, modification of surface material characteristics (oxidation, doping, ion implantation etc.), chemical-mechanical polishing (CMP), and so forth. The apparatus 226 may, in practice, represent a series of different processing steps performed in one or more apparatuses. As another example, apparatus and processing steps may be provided for the implementation of selfaligned multiple patterning, to produce multiple smaller features based on a precursor pattern laid down by the lithographic apparatus.

[0019] As is well known, the manufacture of semiconductor devices involves many repetitions of such processing, to build up device structures with appropriate materials and patterns, layer-by-layer on the substrate. Accordingly, substrates 230 arriving at the litho cluster may be newly prepared substrates, or they may be substrates that have been processed previously in this cluster or in another apparatus entirely. Similarly, depending on the required processing, substrates 232 on leaving apparatus 226 may be returned for a subsequent patterning operation in the same litho cluster, they may be destined for patterning operations in a different cluster, or they may be finished products to be sent for dicing and packaging.

[0020] Each layer of the product structure requires a different set of process steps, and the apparatuses 226 used at each layer may be completely different in type. Further, even where the processing steps to be applied by the apparatus 226 are nominally the same, in a large facility, there may be several supposedly identical machines working in parallel to perform the step 226 on different substrates. Small differences in set-up or faults between these machines can mean that they influence different substrates in different ways. Even steps that are relatively common to each layer, such as etching (apparatus 222) may be implemented by several etching apparatuses that are nominally identical but working in parallel to maximize throughput. In practice, moreover, different layers require different etch processes, for example chemical etches, plasma etches, according to the details of the material to be etched, and special requirements such as, for example, anisotropic etching.

[0021] The previous and / or subsequent processes may be performed in other lithography apparatuses, as just mentioned, and may even be performed in different types of lithography apparatus. For example, some layers in the device manufacturing process which are very demanding in parameters such as resolution and overlay may be performed in a more advanced lithography tool than other layers that are less demanding. Therefore, some layers may be exposed in an immersion type lithography tool, while others are exposed in a ‘dry’ tool. Some layers may be exposed in a tool working at DUV wavelengths, while others are exposed using EUV wavelength radiation.

[0022] In order that the substrates that are exposed by the lithographic apparatus are exposed correctly and consistently, it is desirable to inspect exposed substrates to measure properties such as overlay errors between subsequent layers, line thicknesses, critical dimensions (CD), etc. Accordingly, a manufacturing facility in which litho cell LC is located also includes a metrology system which receivessome or all of the substrates W that have been processed in the litho cell. Metrology results are provided directly or indirectly to the supervisory control system SCS. If errors are detected, adjustments may be made to exposures of subsequent substrates, especially if the metrology can be done soon and fast enough that other substrates of the same batch are still to be exposed. Also, already exposed substrates may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on substrates that are known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures can be performed only on those target portions which are good.

[0023] Also shown in Figure 1 is a metrology apparatus 240 which is provided for making measurements of parameters of the products at desired stages in the manufacturing process. A common example of a metrology station in a modem lithographic production facility is a scatterometer, for example a dark-field scatterometer, an angle-resolved scatterometer or a spectroscopic scatterometer, and it may be applied to measure properties of the developed substrates at 220 prior to etching in the apparatus 222. Using metrology apparatus 240, it may be determined, for example, that important performance parameters such as overlay or critical dimension (CD) do not meet specified accuracy requirements in the developed resist. Prior to the etching step, the opportunity exists to strip the developed resist and reprocess the substrates 220 through the litho cluster. The metrology results 242 from the apparatus 240 can be used to maintain accurate performance of the patterning operations in the litho cluster, by supervisory control system SCS and / or control unit LACU 206 making small adjustments over time, thereby minimizing the risk of products being made out-of-specification, and requiring re-work.

[0024] Additionally, metrology apparatus 240 and / or other metrology apparatuses (not shown) can be applied to measure properties of the processed substrates 232, 234, and incoming substrates 230. The metrology apparatus can be used on the processed substrate to determine important parameters such as overlay or CD.

[0025] A metrology apparatus suitable for use in embodiments of the invention is shown in Figure 2(a). A target T and diffracted rays of measurement radiation used to illuminate the target are illustrated in more detail in Figure 2(b). The metrology apparatus illustrated is of a type known as a dark field metrology apparatus. The metrology apparatus may be a stand-alone device or incorporated in either the lithographic apparatus LA, e.g., at the measurement station, or the lithographic cell LC. An optical axis, which has several branches throughout the apparatus, is represented by a dotted line O. In this apparatus, light emitted by source 11 (e.g., a xenon lamp) is directed onto substrate W via a beam splitter 15 by an optical system comprising lenses 12, 14 and objective lens 16. These lenses are arranged in a double sequence of a 4F arrangement. A different lens arrangement can be used, provided that it still provides a substrate image onto a detector, and simultaneously allows for access of an intermediate pupil-plane for spatial -frequency filtering. Therefore, the angular range at which the radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane, here referred to as a (conjugate) pupil plane. Inparticular, this can be done by inserting an aperture plate 13 of suitable form between lenses 12 and 14, in a plane which is a back -projected image of the objective lens pupil plane. In the example illustrated, aperture plate 13 has different forms, labeled 13N and 13S, allowing different illumination modes to be selected. The illumination system in the present examples forms an off-axis illumination mode. In the first illumination mode, aperture plate 13N provides off-axis from a direction designated, for the sake of description only, as ‘north’. In a second illumination mode, aperture plate 13S is used to provide similar illumination, but from an opposite direction, labeled ‘south’. Other modes of illumination are possible by using different apertures. The rest of the pupil plane is desirably dark as any unnecessary light outside the desired illumination mode will interfere with the desired measurement signals.

[0026] As shown in Figure 2(b), target T is placed with substrate W normal to the optical axis O of objective lens 16. The substrate W may be supported by a support (not shown). A ray of measurement radiation I impinging on target T from an angle off the axis O gives rise to a zeroth order ray (solid line 0) and two first order rays (dot-chain line +1 and double dot-chain line -1). It should be remembered that with an overfilled small target, these rays are just one of many parallel rays covering the area of the substrate including metrology target T and other features. Since the aperture in plate 13 has a finite width (necessary to admit a useful quantity of light, the incident rays I will in fact occupy a range of angles, and the diffracted rays 0 and +1 / -1 will be spread out somewhat. According to the point spread function of a small target, each order + 1 and - 1 will be further spread over a range of angles, not a single ideal ray as shown. Note that the grating pitches of the targets and the illumination angles can be designed or adjusted so that the first order rays entering the objective lens are closely aligned with the central optical axis. The rays illustrated in Figures 2(a) and 2(b) are shown somewhat off axis, purely to enable them to be more easily distinguished in the diagram.

[0027] At least the 0 and +1 orders diffracted by the target T on substrate W are collected by objective lens 16 and directed back through beam splitter 15. Returning to Figure 2(a), both the first and second illumination modes are illustrated, by designating diametrically opposite apertures labeled as north (N) and south (S). When the incident ray I of measurement radiation is from the north side of the optical axis, that is when the first illumination mode is applied using aperture plate 13N, the +1 diffracted rays, which are labeled +1(N), enter the objective lens 16. In contrast, when the second illumination mode is applied using aperture plate 13S the -1 diffracted rays (labeled -1(S)) are the ones which enter the lens 16.

[0028] A second beam splitter 17 divides the diffracted beams into two measurement branches. In a first measurement branch, optical system 18 forms a diffraction spectrum (pupil plane image) of the target on first sensor 19 (e.g. a CCD or CMOS sensor) using the zeroth and first order diffractive beams. Each diffraction order hits a different point on the sensor, so that image processing can compare and contrast orders. The pupil plane image captured by sensor 19 can be used for many measurement purposes such as reconstruction used in methods described herein. The pupil plane image can also beused for focusing the metrology apparatus and / or normalizing intensity measurements of the first order beam.

[0029] In the second measurement branch, optical system 20, 22 forms an image of the target T on sensor 23 (e.g. a CCD or CMOS sensor). In the second measurement branch, an aperture stop 21 is provided in a plane that is conjugate to the pupil -plane. Aperture stop 21 functions to block the zeroth order diffracted beam so that the image of the target formed on sensor 23 is formed only from the - 1 or +1 first order beam. The images captured by sensors 19 and 23 are output to processor PU which processes the image, the function of which will depend on the particular type of measurements being performed. Note that the term ‘image’ is used here in a broad sense. An image of the grating lines as such will not be formed, if only one of the -1 and +1 orders is present.

[0030] The particular forms of aperture plate 13 and field stop 21 shown in Figure 2 are purely examples. In another embodiment of the invention, on-axis illumination of the targets is used and an aperture stop with an off-axis aperture is used to pass substantially only one first order of diffracted light to the sensor. In yet other embodiments, 2nd, 3rdand higher order beams (not shown in Figure 2) can be used in measurements, instead of or in addition to the first order beams.

[0031] The target T may comprise a number of gratings, which may have differently biased overlay offsets in order to facilitate measurement of overlay between the layers in which the different parts of the composite gratings are formed. The gratings may also differ in their orientation, so as to diffract incoming radiation in X and Y directions. In one example, a target may comprise two X-direction gratings with biased overlay offsets +d and -d, and Y -direction gratings with biased overlay offsets +d and -d. Separate images of these gratings can be identified in the image captured by sensor 23. Once the separate images of the gratings have been identified, the intensities of those individual images can be measured, e.g., by averaging or summing selected pixel intensity values within the identified areas. Intensities and / or other properties of the images can be compared with one another. These results can be combined to measure different parameters of the lithographic process.

[0032] Figure 3 shows a device manufacturing arrangement for making bonded substrates (and therefore ICs based on bonded substrates) comprising a first manufacturing lithocell LC 1 and a second manufacturing lithocell LC2. Within each lithocell is a pair of lithographic processing systems 300a, 300b and first metrology systems 310a, 310b. The lithographic processing system 300a, 300b, may comprise a full patterning system. Such a system may comprise, for example, an optical lithographic apparatus or scanner such as described in respect of Figure 1, a track tool, a deposition tool, an etch tool, any other apparatus used in the patterning process, or any combination selected therefrom. The systems may also each comprise a software application 320a, 320b in communication with its respective lithographic processing system 300a, 300b and metrology system 310a, 310b, so that results, designs, data, etc. of the lithographic processing system 300a, 300b and / or the metrology apparatus 310a, 310b may be stored and analyzed by the software application 320a, 320b at the same time or different times.

[0033] Once pairs of substrates or wafers are completed from each of lithocell LC 1 and lithocell LC2, they may be bonded within a bonding tool 330 to obtain a bonded wafer. Bonding in this context is wafer-to-wafer bonding where whole wafers are aligned and bonded together such that individual dies on each wafer are aligned. The concept of wafer-to-wafer bonding is known and used in many IC manufacturing processes. The bonding tool 330 may comprise a bonding alignment device for aligning the wafers together for bonding. For example, the bonding tool 330 may perform pre -align using box- in-box marks provided to wafers (e.g., one box on each wafer), with visual inspection of marks used for alignment quality / position control. Another method uses two imaging sensors (e.g., face to face) which are first calibrated together to find their relative positions; each sensor is then used to separately align a respective wafer to be bonded.

[0034] Lithocell LC1 and lithocell LC2 may be the same lithocell, different lithocells but comprising one or more shared tools and elements, or be completely different lithocells having completely different sets of apparatuses and tools, possibly even at different sites or fabs. For example, one or more of the tools or apparatuses of the lithographic processing systems 300a and 300b may comprise different tools or the same tools within each respective system. Similarly, metrology apparatuses 310 and 310b may be the same apparatus or different apparatuses. The software application 320a, 320b may be comprised within one or both of the respective lithographic processing systems 300a, 300b and / or one or both of the first metrology systems 310a, 310b, or elsewhere.

[0035] Once bonded, the bonded wafer may be subject to further lithographic patterning and processing (such as grinding). As such, alignment will be performed on the bonded wafer; e.g., for aligning the substrate and determining feed-forward corrections based on measured grid deformities. Also, post-exposure metrology, such as overlay metrology, may be performed on the bonded wafer after exposure; e.g., to determine feedback corrections for subsequent wafers.

[0036] Wafer-to-wafer (or substrate-to-substrate) bonding has gained increased attention owing to the possibilities it brings to enable advancements in the semiconductor industry. A typical wafer-to-wafer bonding process may comprise joining (i.e., bonding) two substrates to one another, and in some cases applying physical pressure, temperature and / or an electric field to facilitate bonding.

[0037] A typical wafer-to-wafer bonding method may comprise using a center pin (i.e., a physical pin that contacts the center of a donor and / or acceptor substrate) to initiate a bonding process and subsequently the bonding propagates from the center of a substrate to the substrate edge. There are several challenges associated with wafer-to-wafer bonding. The control of a bonding procedure and the strength of the bonds between bonded wafers are important factors that may contribute to a bonding fingerprint (e.g., a physical distortion in a bonded wafer stack) and enable further processing.

[0038] Hardware solutions offered by bonding tool manufacturers may include bonding tool “control knobs” such as a bonding initiating pin, or center pin (i.e., a physical pin that engages a substrate to initiate a bonding process), or pressure / vacuum tuning to enhance a bonding process. However, state of the art methods are not sufficient to ensure a homogeneous, low and / or correctable bonding fingerprintacross a wafer. For example, after bonding, in order to induce strong covalent bonds, high temperature treatment may be required. High temperature treatment may have a detrimental effect to device features present on a bonded wafer. A physical center pin may introduce a distortion “fingerprint” which may be difficult to correct. Further, present methods may not provide control (e.g., of a speed) over a bonding wavefront through the wafer radius (i.e., varying from a center of the wafer towards a wafer edge).

[0039] One such typical bonding technique that has been implemented to bond semiconductor substrates (often referred to as wafers) is fusion bonding. Fusion bonding enables permanent connection via dielectric layers on each bonding semiconductor substrate and provides a good bonding strength with a high bonding yield. Typically, the fusion bonding process comprises three main steps: 1) wafer surface preparation which may include surface planarization, cleaning and activation; 2) pre -bonding at room temperature which may include aligning the two bonding surfaces; and 3) annealing (or heat treatment) at elevated temperatures (e.g., 200°C to 500°C). In some examples, spontaneous adhesion of the two bonding surfaces occurs at room temperature via hydrogen bridge bonds of chemisorbed water molecules which react during the annealing step to form covalent siloxane bonds. Further information about the fusion bonding technique can be found in the book “Handbook of Wafer Bonding” edited by Peter Ramm, James J.-Q. Lu, and Maaike M. V. Taklo, published by Wiley -VCH, 11 January 2012, ISBN 9783527326464, which is incorporated herein by reference.

[0040] WO2019066814, US2019229082, US2013140713 and WO2023235163 disclose the use of self-assembled monolayers (SAMs) in treating substrates to provide a hydrophilic surface and are incorporated herein by reference.

[0041] FR2915624 and CN108054087 describe local heating of a substrate to locally control the speed of a bonding wave and are incorporated herein by reference.

[0042] Modifying a substrate region specific property of a substrate surface to be bonded may influence the homogeneity of a wafer-to-wafer, or substrate-to-substrate bonding process (i.e., the rate at which a bonding wave propagates during a bonding process impacts the post bonding distortion fingerprint. A slower and more controlled bonding wavefront may provide a smaller fingerprint). A metric that may serve to indicate an effectiveness (e.g., homogeneity) of a wafer-to-wafer bonding process may be the hydrophobicity of bonding surfaces. That is, a hydrophobic bonding surface may provide for homogenous bonding between two wafer surfaces to be bonded.

[0043] A known method for modifying a region-specific property of e.g., a substrate or wafer, is the treatment of said wafer or substrate to form self-assembled monolayers (SAMs). SAMs may effectively passivate of functionalize a surface thus applying a substrate region specific property such as tuning hydrophobicity by forming ordered organic films (e.g., from a solution or a vapour phase). Selfassembled monolayers (SAMs) may be defined as ordered molecular assemblies formed spontaneously by the adsorption of a surfactant with a specific “head” group, or head, of molecules with a particular chemical affinity to the surface to be modified.

[0044] With reference to Figure 4, a SAM 400 may comprise a functional head group of molecules 410, or head, that forms close to a substrate 440, a functional end group of molecules known as a tail group 420, or tail, that forms distal from the substrate 440 relative to the head 410, and a body 430 connecting the head group 410 and the tail group 420. Said functionality may be already present or activated by e.g., thermal activation (heating) or ultraviolet (UV) radiation activation.

[0045] Some example processes available for treating a surface (e.g., of a substrate) to form SAMs include inducing OH groups and hydrophilicity with oxygen plasma and / or substrate priming with alkylsilane (e.g., hexamethyldisilazane (HMDS)) to create a hydrophobic surface with strong covalent bonds.

[0046] SAMs may be configured with a chemical property such as a chemical affinity to surfaces comprising silicon (Si), silicon oxide (SiOx), gold (Au), metal -oxides and the like. Adsorbates used as SAMs may comprise, for example, Si containing heads as used on Si / SiOx surfaces, phosphoric or carboxylic acid containing heads used on metal-oxides, and thiol (e.g., SH) containing heads used on gold surfaces.

[0047] Treated surfaces (e.g., a substrate surface) comprising SAMs can be characterized (e.g., to determine hydrophobicity) with methods such as contact angle goniometry, ellipsometry, atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and the like. A relatively high contact angle (e.g., with respect to a water droplet disposed on a treated surface) may indicate a relatively hydrophobic surface, and a relatively low contact angle may indicate a relatively hydrophilic surface.

[0048] To obtain a substrate region specific property such as a desired level of hydrophobicity and / or desired chemical properties, a substrate may be treated with a mixture of SAMs (e.g., comprising different head 410, body 430, and / or tail 420 groups).

[0049] Owing to functional tail groups, SAMs with a chemical affinity to one another have been used to form strong covalent bonds. In an example of a desirable chemical property, SAM modified nanoparticles have been shown to bond to SAM modified surfaces by using variations of “click” chemistry (i.e., a high-yield reaction joining two molecular entities) and / or ligand exchange (i.e., a reaction in which a headgroup ligand attached to a wafer is replaced by tail group ligand of SAM attached to other wafer.

[0050] Some specific examples of SAM tail groups having a chemical affinity to another SAM tail group or a surface (e.g., of a substrate) are: an azide (e.g., Ns) terminated SAM (i.e., a SAM comprising an azide tail group) may have an affinity to an ethynyl (e.g., CCH) terminated SAM; a SAM comprising a carboxylic acid (e.g., COOH) or phosphoric acid (e.g., (O)PO(OH)2) tail group may have an affinity to a metal -oxide surface; and / or a SAM comprising a thiol (e.g., SH) tail group may have an affinity to a gold surface.

[0051] Some specific examples of SAMs that may be used to modify a surface (e.g., of a substrate) to tune a hydrophilicity of said surface may comprise azide (e.g., N2H), hydroxyl (e.g., OH) and / or carboxyl (e.g., COOH) tail groups.

[0052] The present inventors have devised methods to exploit the properties of SAMs in order to solve the afore-mentioned problems related to wafer-to-wafer bonding. In this way, there may be provided a controlled, homogenous, low temperature, low fingerprint and reproduceable wafer-to-wafer bonding process. In some cases, tuning a hydrophobicity of a substrate surface may serve as a “control knob” to effectively mitigate a bonding fingerprint.

[0053] That is, by applying a substrate region specific property to a treated surface of a donor and / or acceptor substrate, it may be possible to locally control the evolution of a bonding wave (e.g., the speed at which the bonding wave propagates), e.g., by inducing and / or tuning a hydrophobicity of said donor and / or acceptor substrate, thus reducing a bonding fingerprint. SAMs comprising tails groups comprising a chemical property such as a chemical affinity to one another (e.g., by click chemistry or ligand exchange) or tails groups comprising a chemical property such as a chemical affinity to a particular surface (e.g., of an acceptor or donor substrate) may be used to achieve strong covalent bonding between a donor and an acceptor substrate, advantageously without performing an annealing step.

[0054] With reference to Figure 5, in some examples applying a substrate region specific property to a treated surface of a donor and / or acceptor substrate 500 may comprise treating said donor and / or acceptor substrate 500 to provide a hydrophilic region 510. Said hydrophilic region 510 may in some examples act as a chemical center pin during a wafer-to-wafer bonding process that may not induce a physical distortion (i.e., in contrast to a physical center pin), and operates to initialize a bonding wave from the center of said donor and / or acceptor substrate 500.

[0055] In some examples, hydrophilic region 510 may be substantially circular in shape. Hydrophilic region 510 may further be substantially located at a central region of the substrate 500, and / or comprising a common center with substrate 500. It will be understood that although Figure 5 shows a substantially circular substrate, a substrate may comprise any shape as required by any particular use case. Thus, said hydrophilic region 510 may be substantially located at a central region of a substrate 500 or comprise a common center with substrate 500 regardless of the shape of substrate 500.

[0056] In some examples, said hydrophilic region 510 may be substantially circular region located concentrically on substrate 500.

[0057] Said applying a substrate region specific property to a treated surface of a donor and / or acceptor substrate 500 may further comprise treating remaining parts of said donor and / or acceptor substrate 500 (i.e., remaining parts not including the center) to provide a hydrophobic region 520. Said hydrophobic region 520 may serve to provide an enhanced bond between a donor and an acceptor substrate in a bonding process.

[0058] With reference to Figure 6. in a further example applying a substrate region specific property to a treated surface of a donor and / or acceptor substrate 500 may comprise applying a substrate region specific property throughout a radius of said donor and / or acceptor substrate 500. That is, it may be beneficial to have an amount of control over how a bonding wave propagates through the radius of said donor and / or acceptor substrate 500. This may be achieved by applying a substrate region specific property to a plurality of different substrate regions 600 610 620 630 along the donor and / or acceptor substrate 500 radius (e.g., from the center outwards towards the substrate edge) to provide bonding control (e.g., velocity control). Said substrate region specific property may comprise a hydrophobicity and / or hydrophilicity. In some examples, a level of hydrophobicity may increase from the center of a donor and / or acceptor substrate 500, said hydrophobicity increasing towards the outward edge of said donor and / or acceptor substrate 500. By tuning a level of hydrophobicity in each of the plurality of different substrate regions 600 610 620 630 it may be possible to control a speed of a bonding wave during a wafer-to-wafer bonding process.

[0059] In some examples, plurality of different substrate regions 600 610 620 630 may be substantially circular in shape. The plurality of different substrate regions 600 610 620 630 may further comprise a common center with substrate 500. It will be understood that although Figure 6 shows a substantially circular substrate, a substrate may comprise any shape as required by any particular use case. Thus, said plurality of different substrate regions 600 610 620 630 may comprise a common center with substrate 500 regardless of the shape of substrate 500. In some examples, said plurality of different substrate regions 600 610 620 630 may be located concentrically on substrate 500.

[0060] In any or all examples, said treated surface of a donor and / or acceptor substrate 500 comprise SAMs. That is, said donor and / or acceptor substrate 500 may comprise SAMs configured to provide a substrate region specific property on said donor and / or acceptor substrate 500. Said substrate region specific property may comprise a hydrophobicity, hydrophilicity or chemical property.

[0061] With reference to Figure 7A, a first substrate region 710 (e.g., of a first donor and / or acceptor substrate) may be treated by application of a first SAM 725 comprising a first end group 715 and first tail group 720. The first end group 715 may have a chemical affinity to the first substrate region 710. With reference to Figure 7B, a second substrate region 730 (e.g., of a second donor and / or acceptor substrate) may be treated by application of a second SAM 745 comprising a second end group 735 and second tail group 740. The second end group 735 may have a chemical affinity to the second substrate region 730. The first and second substrate regions 710 730 may in some examples comprise the same material. Thus, in some examples the first end group 715 and second end group 735 may comprise the same functional group of molecules. In other examples, the first and second substrate regions 710 730 may comprise different material. In such examples, the first end group 715 and second end group 735 may each comprise a different functional group of molecules, each with a chemical affinity to the corresponding first and / or second substrate regions 710 730.

[0062] Said first SAM 725 and / or second SAM 745 may be configured to provide a substrate region specific property to corresponding first and / or second substrate regions 710 730. In some examples, said substrate region specific property may comprise a hydrophobicity and / or a hydrophilicity.

[0063] With reference to Figure 7C, said first substrate region 710 and second substrate region 730 may be comprised in a donor / acceptor substrate pair (i.e., a donor and acceptor substrate to be bonded together). Said first tail group 720 and second tail group 740 may be configured to have a chemical affinity to one another. That is, the first tail group 720 may comprise a first functional group of molecules with a chemical affinity to a second functional group of molecules comprised in the second tail group 740. In this way, said first tail group 720 and second tail group 740 may be configured to form a strong covalent bond during a substrate-to-substrate bonding process. In some examples, said covalent bond may be formed by click chemistry. In other examples, said covalent bond may be formed by ligand exchange.

[0064] With reference to Figures 8A and 8B, in any or all examples a first processed substrate region 810 may comprise a first processed surface 820 and a second processed substrate region 840 may comprise a second processed surface 850. First processed surface 820 may be treated by application of a SAM 835 comprising a head group 825 comprising a group of molecules configured to have a chemical affinity to the first processed surface 820 and a tail group 830 comprising a group of molecules configured to have a chemical affinity to the second processed surface 850. In this way, a surface of one of a donor and / or acceptor substrate in a wafer-to-wafer bonding process (i.e., first processed surface 820 or second processed surface 850) may be treated (e.g., by application of a SAM 835). Referring to Figure 8C, during a bonding process tail group 830 may form a bond to second processed surface 850, thus forming an effective head group on second processed surface 850. A type of SAM 835 may be selected and / or configured, (e.g., selection and / or configuration of head group 825 and / or tail group 830) based on a chemical affinity of the first and / or second processed surface 820 850.

[0065] It may be noted that in the examples shown in Figures 7A-7C, any of first substrate region 710 and second substrate region 730 may also comprise a processed substrate region comprising a processed surface (e.g., any of first or second processed substrate regions 710 740 and / or first or second processed surfaces 720 750).

[0066] With reference to Figure 9, in any or all examples a plurality of different SAMs (e.g., SAMs 910 920 930) may be applied to a substrate 900 (e.g., any of first substrate region 710, second substrate region 730, first processed surface 820 or second processed surface 850). By applying a plurality of different SAMs 910 920 930, for example comprising different head and / or tail groups, it may be possible to tune any combination of a chemical property, hydrophobicity or hydrophilicity of said substrate (e.g., to facilitate wafer-to-wafer bonding by providing applying a substrate region specific property such as hydrophobicity whilst also providing for covalent bonding between a donor / acceptor substrate pair).

[0067] In some examples, a plurality of different SAMs 910 920 930 with varying tail groups may be provided on a surface of a first donor and / or acceptor substrate (e.g., first and / or second processed surface 820 850) to enable bonding to different areas of a second donor and / or acceptor substrate which may have regionally different types of surfaces.

[0068] Owing to the nature and choices of semiconductor processing steps, donor and / or acceptor substrates may have different features and / or surfaces (e.g., comprising formed devices, different carrier types, surfaces comprising silicon, oxides, metal dominated surfaces and the like). Thus, SAM types and / or configurations may be selected accordingly.

[0069] In some examples, a first SAM (e.g., SAM 910) of a plurality of SAMs 910 920 930 may be configured to provide a level of hydrophobicity, hydrophilicity or a chemical property, and a second SAM (e.g., SAM 920) may be configured to provide covalent bonding (e.g., by switch chemistry or ligand exchange) with a corresponding SAM on a corresponding substrate (e.., a donor and / or acceptor substrate) during a wafer-to-wafer bonding process.

[0070] In any or all examples, SAMs may be applied to a substrate in the form of a solution or from vapor deposition on to surfaces activated by e.g., by short oxygen plasma treatment. In some examples, a reaction forming said SAMs may be accelerated by heating a substrate (e.g., up to 50 degrees Celsius).

[0071] Referring back to Figure 5 and Figure 6, a treated surface of a donor and / or acceptor substrate 500 may comprise SAMs formed on said donor and / or acceptor substrate 500 in accordance with any or all examples. Said applying a substrate region specific property may comprise configuring said SAMs to provide a substrate region specific hydrophobicity, hydrophilicity and / or chemical property on a corresponding substrate region.

[0072] With further reference to Figures 5 and 6, when said treated surface comprises SAMs, applying a substrate region specific property to a treated surface of a donor and / or acceptor substrate 500 throughout a radius of said donor and / or acceptor substrate 200 may comprise configuring a hydrophobicity, hydrophilicity and / or chemical property of said SAMs on a corresponding substrate region. Said configuration of a hydrophobicity, hydrophilicity and / or chemical property of a SAM through a radius of a donor and / or acceptor substrate 500 may comprise temperature treatment of said donor and / or acceptor substrate during the formation of said SAMs.

[0073] For example, a particular level of hydrophobicity may be achieved by heating a substrate region during deposition and / or forming of SAMs, or post forming of SAMs. Relatively hotter regions may attract more molecules resulting in relatively higher hydrophobicity. A temperature range from 0 to 100 degrees may be suitable for tuning hydrophobicity whilst not harming any device structures present on a processed substrate.

[0074] By providing a temperature gradient throughout a radius of said donor and / or acceptor substrate 500 during SAM formation and / or deposition, a varying local (i.e., substrate region specific) property such as hydrophobicity, hydrophilicity and / or chemical property may be realized. By tuning a substrate region specific property in each of a plurality of different substrate regions (e.g., substrate regions 600610 620 630) it may be possible to provide enhanced control (e.g., of a speed of a bonding wave) during a wafer-to-wafer bonding process.

[0075] In some examples, said configuration of a hydrophobicity, hydrophilicity and / or chemical property of a SAM through a radius of a donor and / or acceptor substrate 500 may comprise UV treatment of said substrate. That is, UV radiation may be applied to a substrate in order to configure a hydrophobicity, hydrophilicity and / or chemical property of a SAM through a radius of a donor and / or acceptor substrate 500. Different intensities of UV radiation may be provided to different substrate regions in order to locally configure, or tune, said hydrophobicity, hydrophilicity and / or chemical property on a substrate.

[0076] Although Figure 5 and Figure 6 show a “bullseye” type configuration of concentric substrate regions 510 520, 600 610 620 630, it will be understood by the skilled person that a substrate may comprise different surface terminations, such as comprising device features and / or surface types (e.g., comprising formed devices, different carrier types, surfaces comprising silicon and / or oxides, metal dominated surfaces and the like). Different features and / or surfaces of a substrate may result in a different shape configuration of substrate regions comprising any suitable variation of different treated surfaces (e.g., by SAM application) as determined by any particular use case.

[0077] In any or all examples, in order to increase a contrast between treated substrate regions (e.g., substrate regions 510 520, 600 610 620 630), SAMs may be applied per-region by shielding parts of the substrate during SAM formation and / or deposition. For example, a shield, or mask, may be formed e.g., from glass, silicone or any other suitable material that may act as a physical barrier against a SAM to be deposited and is compatible (e.g., chemically compatible) with said substrate. Said shield or mask may be disposed in close proximity to, or direct contact with, a substrate. A SAM may be deposited (e.g., from a vapor phase) onto the masked substrate, allowing SAM deposition onto regions of the substrate not shielded. This process may be performed a plurality of times e.g., using different shaped masks in order to provide a plurality of different surface terminations (e.g., on substrate regions 510 520, 600 610 620 630).

[0078] In atypical bonding process, a donor and / or acceptor substrate 500 may be aligned with respect to one another, after which the bonding process is initiated (e.g., by a vacuum at the center of the donor and / or acceptor substrate 500 inducing the substrates to make contact). The contacting areas between the two substrates area then propagates form the initiation point towards the edge of the wafer (i.e., the bonding wavefront). In the case of patterned wafers, the shape of the wavefront make take the shape of features on the patterned substrate. For example, if the substrate comprises a rectangular die, the wavefront will take the form of a rectangle. This example is described reference to Figure 10. At a first time 1010, the bonding wavefront takes the form of a rectangle with rounded edges. The bonding wave propagates towards the edges of donor and / or acceptor substrate 500 maintaining the rectangular shape e.g., at second time 1011 and third time 1012. Thus, the bonding wavefront is not equally distributed with respect to the donor and / or acceptor substrate 500. The comers of the rectangular bondingwavefront reach the substrate edge before the edges of the rectangular bonding wavefront, which may lead to e.g., overlay and / or alignment errors.

[0079] Typically, a substrate to be bonded may be subject to surface treatments such as a plasma treatment prior to bonding. Surface treatments such as plasma treatments may result in broken bonds, or dangling bonds, at the surface of the substrate. Typically, when rinsing a substrate e.g., with water, the broken bonds react and turn into a hydroxyl (OH) group. Hence, the treatment results in an OH terminated surface of the substrate, which may yield a high energy surface. Dangling bonds may be defined as unsatisfied valence on an immobilized atom (e.g., comprised at the surface of a donor and / or acceptor substrate). Surface free energy (SFE) is the energy that results from dangling bonds which are exposed at the surface of a material, and influences the propagation of a bonding wavefront. The SFE represents the work that would be necessary to increase the surface area of a solid phase. SFE has a decisive influence on the wettability of solids by liquids. It is therefore an important parameter for the optimization of coating processes, but also for any other type of solid-liquid contact. Typically, for an initial bond formation, hydroxyl groups on both donor and acceptor substrates are used, and hence a high surface free energy is required. Moreover, the propagation of the wavefront during the bonding process depends partially on the surface free energy. As such, bond formation and the propagation of a bond between a donor and an acceptor substrate can be regulated by the surface free energy.

[0080] By modifying a density of dangling bonds it is possible to modify the surface free energy of a donor and / or acceptor substrate and thus provide some control over a bonding process (e.g., velocity of a bonding wave). Accordingly, in order to provide a homogenous bonding wavefront, a further example of treating a surface of a donor and / or acceptor substrate 500 may comprise modifying a density of dangling bonds on the surface of the donor and / or acceptor substrate 500.

[0081] In some examples, modifying a density of dangling bonds on the surface of the donor and / or acceptor substrate 500 may comprise providing a gradient in the density of dangling bonds across the surface of the donor and / or acceptor substrate.

[0082] With reference to Figure 11, and continuing with the example of a rectangular bonding wavefront, a surface of donor and / or acceptor substrate 500 may be modified based on a predicted, modelled and / or measured bonding wavefront to counteract an uneven distribution of said bonding wavefront.

[0083] In some typical pre-bonding processes, a plasma activation step may be performed to prepare a surface of a donor and / or acceptor substrate 500 to be bonded. The purpose of said typical plasma activation step is to clean the substrate surface from organic contaminants. Plasma treatment of a surface of a donor and / or acceptor substrate 500 may modify a density of dangling bonds comprised on a surface of said donor and / or acceptor substrate 500, thus modifying the surface free energy of said substrate,impacting the velocity of a bonding wavefront (e.g., the substantially rectangular bonding wavefront of Figure 10).

[0084] Aspects of the present disclosure may comprise treating a donor and / or acceptor substrate with plasma in order to modify the surface free energy of said donor and / or acceptor substrate based on a predicted, modelled and / or measured bonding wavefront (i.e., of an untreated donor and / or acceptor substrate) to provide a plasma modified region 1101 on a surface of the donor and / or acceptor substrate . Said modified surface is configured, based on the predicted, modelled and / or measured bonding wavefront, to provide a homogenous bonding wavefront during a subsequent bonding process. That is, the velocity at which the bonding wavefront propagates towards the edge of the wafer may be modified in regions of the substrate (i.e., plasma modified region 1101) to provide a homogenous bonding wavefront.

[0085] In some examples, the plasma may be applied to the donor and / or acceptor substrate in a pattern that is the inverse of a pattern of the predicted, modelled and / or measured bonding wavefront.

[0086] In some examples, a gradient of the surface free energy of a donor and / or acceptor substrate 500 may be modified by plasma treatment using, for example, any combination of argon (Ar), hydrogen (H2), oxygen (O2). nitrogen (N2), nitrous oxide (N2O) and / or water (H2O) gases excited to a plasma state. In some examples, a gradient of the surface free energy of a donor and / or acceptor substrate 500 may be modified by varying a power of said plasma treatment. That is, the plasma may be adjusted (e.g., gas content and / or power) to change the density of dangling bonds on the surface of the donor and / or acceptor wafer, thus modifying the surface free energy.

[0087] In some examples, the strength of a subsequent bond between two bonded donor and / or acceptor substrates 500 may be adjusted based on controlling the evolution of a bonding wavefront. That is, depending on the surface treatment of the donor and / or acceptor substrate 500, a particular bonding wavefront velocity may provide an optimal bond strength. In a specific example, an oxidized silicon to oxidized silicon bond may have an optimal bonding strength at a lower bonding wavefront velocity than a silicon to silicon bond. Accordingly, a bonding wavefront velocity may be adjusted based on the surface termination of a donor and / or acceptor substrate 500 to provide an optimal bonding strength.

[0088] Said plasma may be an electron cyclotron resonance (ECR) plasma, for example created by using a magnetic field and microwave energy. Such an ESR plasma may be used in a vacuum environment and applied locally to a donor and / or acceptor substrate 500, e.g., in a lateral direction across the surface of a substrate. In atmospheric conditions, an atmospheric plasma source may be used to generate said plasma, such as a plasma jet or a dielectric barrier discharge (DBD) plasma.

[0089] With reference to Figure 12A, in some examples, said plasma may be applied to a donor and / or acceptor substrate 500 surface by using a single plasma source 1210 and scanning the surface of the donor and / or acceptor substrate 500 in two dimensions, e.g., in a raster scan type pattern 1230. Withreference to Figure 12B, in other examples an array of plasma sources 1220 is envisioned, allowing plasma to be applied across a substrate region to be modified in a single scanning direction 1240.

[0090] During some pre-bonding processes, e.g., after a typical plasma treatment process to remove organic contaminants form the surface of a donor and / or acceptor substrate 500 to be bonded, said donor and / or acceptor substrate 500 may be cleaned to remove residue, typically comprising a water-based rinsing process and a drying step. In some cases, after bonding an annealing step may be performed to remove any excess water or air between bonded substrates. The bond strength between two bonded substrates may be determined by H-bond interactions between hydroxyl groups between the surfaces of the donor and / or acceptor substrate 500. Thus, it may be desirable to modify the chemical properties of the surface of a donor and / or acceptor substrate 500 to provide a favorable surface termination promoting a strong bond.

[0091] In some examples, plasma treatment at specific locations on a substrate may be used to attach a SAM at a local position on the substrate. SAMs can be grown at pre-designed positions of a first donor and / or acceptor substrate in order to form a bond with a second donor and / or acceptor substrate. In this way the propagation of a bonding wavefront may be tuned, in addition to correction for bond formation between a donor and an acceptor substrate, as reactants from the donor and acceptor substrate react when they come into contact with each other.

[0092] Other methods of modifying a density of dangling bonds on the surface of a donor and / or acceptor substrate 500 are envisioned. For example, by exposing said donor and / or acceptor substrate 500 to radiation having an energy level suitable for breaking the chemical bonds of the surface termination of said donor and / or acceptor substrate 500 (e.g., radiation as provided by a suitable ultraviolet (UV) and / or electron beam source). Such methods are described in further detail below.

[0093] As mentioned previously, the control of a bonding procedure and the strength of the bonds between bonded wafers are important factors that may contribute to a bonding fingerprint and enable further processing. In some cases, a bonding fingerprint may comprise a magnification, or scaling, error component (i.e., a mismatch in a magnification, or scaling, component of a bonding parameter of interest such as overlay between a donor and acceptor substrate), introduced by, for example, dicing (i.e., the separation of a substrate into individual dies), die warpage or the bonding process itself (e.g., caused by a bonding initiating pin). In particular for die to wafer bonding the individual dies may demonstrate a large scaling / magnification deformation due to the dicing or bonding process (e.g. in particular thin dies may be affected significantly by bonding forces).

[0094] It is known that a magnification, or scaling, error component of a bonding parameter of interest such as overlay may be observed as a function of surface activation, or surface free energy of a substrate, i.e., the density of dangling bonds on the substrate surface as described herein previously. Accordingly, it is possible to control the surface activation of a substrate (in particular a die) prior to a bonding process in order to reduce said magnification, or scaling, error component of a bonding parameter of interest such as overlay.

[0095] Additionally or alternatively to the previously described method of applying a plasma to the surface of a donor and / or acceptor substrate 500 to modify a density of dangling bonds comprised on the surface of said donor and / or acceptor substrate, there is further provided a method comprising applying radiation to the surface of a donor and / or acceptor substrate to modify a density of dangling bonds comprised on the surface of said donor and / or acceptor substrate 500. Said radiation may be configured to have an energy sufficient to break chemical bonds of the surface termination of the donor and / or acceptor substrate 500.

[0096] In a specific, non-limiting example, a surface of a donor and / or acceptor substrate 500 may comprise an Si-0 surface termination. Si-0 comprises a 6 eV bond strength. Accordingly, deep ultraviolet (DUV) radiation of 193nm wavelength comprises sufficient energy (~6.4 eV) to break the Si-0 bond.

[0097] In some examples, said donor and / or acceptor substrate 500 may be irradiated by means of a photomask. In some examples, said photomask may comprise a material that is semi-transparent to the radiation used. The transparency of said photomask may be tuned per-location in order to control the amount of radiation that is incident on the donor and / or acceptor substrate 500. Advantageously, this may allow the entire area of a donor and / acceptor substrate 500 to be illuminated with the same light source. In some examples, said photomask may comprise an adjustable element, for example a spatial light modulator such as a digital mirror device (DMD) configured to adjust an amount of radiation incident on the surface of said donor and / or acceptor substrate 500.

[0098] In a further example, surface activation of a donor and / or acceptor substrate 500 may be provided by means of a scanning spot light source configured to scan across the surface of said donor and / or acceptor substrate 500 at different speeds. In areas where a relatively low surface activation is required a relatively faster scan speed may be used and vice-versa. In this way the surface activation of the donor and / or acceptor substrate 500 may be tuned.

[0099] In other examples, an electron beam (e-beam) source may be configured to locally modify a density of dangling bonds on the surface of a donor and / or acceptor substrate 500. That is, an e-beam source may provide an electron beam with sufficient energy to break surface bonds comprised on the surface of said donor and / or acceptor substrate 500. In this way the surface activation of the donor and / or acceptor substrate 500 may be tuned.

[0100] With reference to Figure 13, in some examples, a method 1300 of determining locations on a surface of a donor and / or acceptor substrate 500 to be modified may comprise measuring 1310 previously manufactured examples of one or more bonded substrates to obtain bonding parameter of interest data relating to a bonding parameter of interest such as overlay in order to determine a grid distortion measurement related to said one or more bonded substrates. That is, locations of overlay errors may be located by dividing the measured bonded substrates into a grid. The error’s location is identified by the grid space that it is located in. Accordingly, surface locations on a donor and / oracceptor substrate 500 to be modified may be determined 1330 from said grid distortion measurements. Said bonding parameter of interest data may comprise a magnification and / or scaling error component.

[0101] In some examples, the determining of surface locations on a donor and / or acceptor substrate 500 to be modified may comprise determining 1320 a model based on the parameter of interest data in order to model and / or predict locations to be modified (i.e., by modifying the density of dangling bonds at said locations).

[0102] Advantageously, a magnification and / or scaling error correction of up to lOppm during a wafer to wafer and / or die to wafer bonding process may be realized by tuning the surface activation of a donor and / or acceptor substrate 500 in accordance with aspects described herein.

[0103] In some examples, based on an initial surface termination of a donor and / or acceptor substrate 500, said substrate 500 may be modified to provide a charged surface termination in order to promote electrostatic bonds upon bonding of the donor and / or acceptor substrate 500. That is, a surface of a donor and / or acceptor substrate 500 may be modified to provide a charged surface having an opposite charge to a surface to be bonded to. In this way, electrostatic bonding may be realized in addition or alternatively to chemical bonding. Advantageously, electrostatic bonding may have a stronger and slower decaying interaction compared to chemical bonding, which makes bond formation more robust to e.g., minute contamination and surface roughness of the surface of a donor and / or acceptor substrate 500.

[0104] With reference to Figure 14, in some examples, said charged surface termination may be provided by rinsing a surface 1410 1420 of a donor and / or acceptor substrate (e.g., donor and / or acceptor substrate 500) with a solution 1430 1440 having a pH level based on an isoelectric point (IEP) of the surface 1410 1420 of said donor and / or acceptor substrate, and drying the surface e.g., by spinning. Methods of providing a charged substrate surface based on a substrate rinsing and drying procedure are further described, for example, in IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. 24, NO. 4, NOVEMBER2011, which is incorporated herein in its entirety by reference.

[0105] Typically, a substrate is charged negatively when the rinsing fluid (e.g., water) has a pH level above an IEP of the substrate and positively when the pH of the rinsing fluid is below the IEP of the substrate. Thus, it is possible to influence the type of charge on a surface of a substrate based on a pH level of a substrate rinsing fluid.

[0106] In other words, a charged surface termination (i.e., positively charged surface termination 1450 and / or negatively charged surface termination 1460) is realized owing to the difference in isoelectric point of the surface of donor and / or acceptor substrate 500 with respect to the pH of the rinsing solution. Depending on said difference in isoelectric point, the surface 1410 1420 of said donor and / or acceptor substrate will become more positively (e.g., Figure 14A) or negatively (e.g., Figure 14B) charged as droplets of the rinsing solution 1430 1440 leave the surface during the drying process.

[0107] In a non-limiting example, an initial surface termination of a first donor and / or acceptor substrate may comprise silicon nitride (SiN), which has an IEP of 6. A second donor and / or acceptor substrate may comprise an initial surface termination of SiO2, which may have an IEP of 3. In the present example, surfaces (e.g., surface 1410 1420) of both the first and second donor and / or acceptor substrates 500 may be rinsed with a solution having a pH level of 5 (e.g., ultrapure water (UPW)) and subsequently dried.

[0108] For the SiN terminated surface, the difference in isoelectric point with respect to the pH level of the rinsing solution leads to a transfer of electrons from the SiN terminated surface to the rinsing solution. During the drying process, the SiN becomes more positively charged as negatively charged droplets leave the surface (e.g., the process described by Figure 14A).

[0109] For the SiO2 terminated surface, the difference in isoelectric point with respect to the pH level of the rinsing solution leads to a transfer of electrons from the rinsing solution to the SiO2 terminated surface. During the drying process, the SiO2 becomes more negatively charged as positively charged droplets leave the surface (e.g., the process described by Figure 14B). Accordingly, after rinsing, the surfaces of the first and second donor and / or acceptor substrates to be bonded will comprise opposite charges. During the bonding process, the positive and negative charges attract each other forming a strong bond. By local rinsing of a donor and / or acceptor substrate (e.g., using an angular rinsing and drying procedure at a typical lab substrate cleaning station), it is possible to provide charged profiles across the surface of a donor and / or acceptor substrate to influence a bonding process.

[0110] It is known that the velocity of a bonding wavefront between a donor and acceptor substrate may be dependent on the pH of a rinsing solution used to rinse said donor and / or acceptor substrate prior to a bonding process. In addition to providing electrostatic bonding by the previously described oppositely charged substrates, in some examples it may be possible to control the velocity of a bonding wavefront between a donor and an acceptor substrate by adjusting a charge on said donor and / or acceptor substrate, for example, by adjusting the surface termination (e.g., type of dielectric) and / or adjusting the pH of a rinsing solution of a donor and / or acceptor substrate. In this way, a specific charge may be defined on the donor and / or acceptor substrate allowing further control of the evolution of a bonding wave between said donor and / or acceptor substrate .

[0111] Advantageously, rinsing of a donor and / or acceptor substrate may be performed locally on a donor and / or acceptor substrate, for example using a typical lab cleaning station. In this way, different amounts of positive and / or negative charges may be realized at different locations on said donor and / or acceptor substrate, thus allowing tuning of a bonding process (e.g., wavefront velocity). Furthermore, the pH of a rinsing solution at each rinsing location may also be varied to further tune the surface properties and thus bonding process.

[0112] Charging typically occurs with low conductivity rinsing fluids (e.g., fluids with a pH between 4 and 10). High conductivity fluids (e.g., with a pH < 3 or > 11), may comprise an amount of charge sufficient to counteract the charging of a substrate surface. Thus, by using a high conductivity rinsingfluid, it may be possible to have zero charge and thus a charge -neutral surface at a specific location on a substrate.

[0113] In some examples, when it is desirable to not alter a bonding wavefront velocity, the surface of a donor and / or acceptor substrate may be rinsed with a solution having a pH to provide a positively and / or negatively charged surface based on maintaining an equal bonding wavefront velocity.

[0114] Further embodiments of the invention are disclosed in the following list of numbered clauses:1. A method for controlling bonding of a donor substrate to an acceptor substrate, the method comprising: treating a surface of the donor and / or acceptor substrate; and applying a substrate region specific property to the treated surface of the donor and / or acceptor substrate to locally control an evolution of a bonding wave.2. The method of clause 1, wherein the substrate region specific property comprises any of a hydrophobicity, hydrophilicity or a chemical property.3. The method of clause 2, wherein the chemical property comprises a chemical affinity of the surface of the donor and / or acceptor substrate to a corresponding surface to be bonded to.4. The method of any previous clause, wherein the step of treating the surface of the donor and / or acceptor substrate comprises forming a self-assembled monolayer on said surface.5. The method of clause 4, wherein the forming a self-assembled monolayer comprises depositing the self-assembled monolayer from a solution and / or from a vapor.6. The method of clause 4 or clause 5, further comprising providing a temperature gradient across the donor and / or acceptor substrate when forming the self-assembled monolayer.7. The method of any previous clause, wherein the step of applying a substrate region specific property comprises applying a temperature gradient across the donor and / or acceptor substrate.8. The method of any previous clause, wherein the step of applying a substrate region specific property comprises applying ultraviolet radiation to the donor and / or acceptor substrate.9. The method of any previous clause, wherein the step of treating the surface of the donor and / or acceptor substrate comprises forming a plurality of self-assembled monolayers on said surface.10. The method of clause 9, wherein at least one first self-assembled monolayer is configured to provide a hydrophobicity, hydrophilicity and / or a chemical property of said surface, and at least one second self-assembled monolayer is configured to provide a chemical affinity to a surface of a donor and / or an acceptor substrate.11. The method of any previous clause, wherein the step of treating the surface of a donor and / or acceptor substrate is based on a termination of said surface.12. The method of any previous clause, further comprising determining a plurality of substrate regions, wherein a substrate region specific property is applied to each of the plurality of substrate regions.13. The method of clause 12, comprising configuring at least one of the plurality of substrate regions to comprise a common center with said donor and / or acceptor substrate.14. The method of clause 13, wherein the substrate region specific property of the at least one of the plurality of substrate regions is hydrophilicity.15 The method of any of clauses 12 to 14, comprising configuring the plurality of substrate regions concentrically on the donor and / or acceptor substrate.16. The method of any of clauses 12 to 15, further comprising applying the substrate region specific property to the plurality of substrate regions to provide an increasing level of hydrophobicity from a center of the donor and / or acceptor substrate towards an outer edge of the donor and / or acceptor substrate.17. The method of any of clauses 12 to 16 wherein the step of applying a substrate region specific property comprises applying a different temperature to each of the plurality of substrate regions.18. The method of any of clauses 12 to 17, wherein the step of applying a substrate region specific property comprises applying ultraviolet radiation of different intensities to each of the plurality of substrate regions.19. The method of any of clauses 12 to 18, wherein the step of treating the surface of the donor and / or acceptor substrate comprises forming at least one self-assembled monolayer on each of the plurality of substrate regions.20. The method of any previous clause, wherein the step of treating a surface of the donor and / or acceptor substrate comprises modifying a density of dangling bonds comprised on the surface of the donor and / or acceptor substrate.21. The method of clause 20, comprising modifying a density of dangling bonds comprised on the surface of the donor and / or acceptor substrate by any of: applying a plasma to the surface of the donor and / or acceptor substrate; or irradiating the surface of the donor and / or acceptor substrate.22. The method of clause 21, further comprising measuring previously manufactured examples of bonded donor and acceptor substrates to obtain bonding parameter of interest data corresponding to a bonding parameter of interest, wherein the density of dangling bonds is modified based on the bonding parameter of interest data.23. The method of clause 22, wherein the bonding parameter of interest comprises a magnification and / or scaling overlay error component.24. The method of any of clause 22 or 23, further comprising determining a model based on the bonding parameter of interest data, wherein the density of dangling bonds is modified based on the model.25. The method of any of clauses 22 to 24, wherein the modifying the density of dangling bonds comprised on the surface of the donor and / or acceptor substrate corrects for the bonding parameter of interest.26. The method of clause 21, comprising modifying the density of dangling bonds based on a predicted, modelled and / or measured bonding wavefront of an untreated donor and / or acceptor substrate.27. The method of clause 26, comprising modifying the density of dangling bonds in a pattern that is the inverse of a pattern of the predicted, modelled and / or measured bonding wavefront.28. The method of any of clauses 21 to 27, further comprising irradiating the surface of the donor and / or acceptor substrate using any of ultraviolet radiation and / or an electron beam.29. The method of any of clauses 21 to 28, further comprising irradiating the surface of the donor and / or acceptor substrate using a scanning spot radiation source and / or a semi-transparent masking device.30. The method of any of clauses 21 to 27, wherein the plasma comprises any of argon, hydrogen, oxygen, nitrogen, nitrous oxide or water.31. The method of any of clauses 21 to 27, further comprising modifying a combination of gasses comprised in the plasma and / or a plasma power at different locations on the surface of the donor and / or acceptor substrate.32. The method of any of clauses 20 to 31 further comprising providing a gradient in the density of dangling bonds across the surface of the donor and / or acceptor substrate.33. The method of any of clauses 20 to 32, wherein the substrate region specific property is a surface free energy of the surface of the donor and / or acceptor substrate.34. The method of any previous clause, wherein the step of treating a surface of the donor and / or acceptor substrate comprises rinsing the donor and / or acceptor substrate in a solution comprising a pH level based on an isoelectric point of the surface of the donor and / or acceptor substrate.35. The method of clause 34, comprising: rinsing the surface of the donor and / or acceptor substrate with a solution comprising a pH level higher than the isoelectric point of the surface of the donor and / or acceptor substrate to provide a negatively charged surface, and / or; rinsing the surface of the donor and / or acceptor substrate with a solution comprising a pH level higher than the isoelectric point of the surface of the donor and / or acceptor substrate to provide a negatively charged surface, and / or rinsing the surface of the donor and / or acceptor substrate with a solution comprising a high conductivity level to provide a charge -neutral surface.36. The method of any of clauses 34 or 35, further comprising providing a negatively charged surface and / or positively charged surface of the donor and / or acceptor substrate to control the evolution of the bonding wave.37. The method of any of clauses 34 to 36 further comprising locally rinsing the surface of the of the donor and / or acceptor substrate to provide a plurality of surface regions the donor and / or acceptor substrate having different amounts of positive and / or negative charge.38. The method of clauses 34 to 37, wherein the substrate region specific property is an electrostatic charge.39. The method of any of clauses 21 to 38, wherein the donor substrate is a die.40. A substrate comprising a treated surface comprising a plurality of substrate regions, wherein at least one of the plurality of the substrate regions comprises a substrate region specific property configured to control the evolution of a bonding wave in a substrate-to-substrate bonding process.41. The substrate of clause 40, wherein the substrate region specific property is any of a hydrophobicity, hydrophilicity or a chemical property.42. The substrate of clause 41, wherein the chemical property comprises a chemical affinity of the surface of the donor and / or acceptor substrate to a corresponding surface to be bonded to.43. The substrate of any of clauses 40 to 42, wherein the at least one of the plurality of substrate regions comprises a self-assembled monolayer.44. The substrate of any of clauses 40 to 43, wherein the treated surface of the substrate comprises a plurality of self-assembled monolayers.45. The substrate of clause 44 comprising at least one first self-assembled monolayer configured to provide a hydrophobicity, hydrophilicity and / or a chemical property of the treated surface, and at least one second self-assembled monolayer configured to provide a chemical affinity to a surface of a donor and / or an acceptor substrate in a substrate-to-substrate bonding process.46. The substrate of any of clauses 40 to 45, wherein at least one of the plurality of substrate regions comprises a common center with said substrate.47. The substrate of any of clauses 40 to 46, wherein the at least one of the plurality of substrate regions comprises a hydrophilic region.48. The substrate of any of clauses 40 to 47, wherein the plurality of substrate regions are arranged concentrically.49. The substrate of any of clauses 40 to 48, configured to provide an increasing level of hydrophobicity from a center of the substrate towards an outer edge of the substrate.50. The substrate of any of clauses 40 to 49, wherein each of the plurality of substrate regions comprise at least one plasma modified region and / or at least one radiation modified region.51. The substrate of clause 50, wherein the at least one plasma modified region and / or at least one radiation modified region comprises a density of dangling bonds different from other regions of the plurality of substrate regions.52. The substrate of clause 51, wherein the density of dangling bonds varies as a gradient across the at least one plasma modified region and / or at least one radiation modified region.53. The substrate of any of clauses 40 to 52, wherein each of the plurality of substrate regions comprise a different positive and / or negative electrostatic charge, said electrostatic charge opposite to an electrostatic charge of a corresponding surface to be bonded to.54. The substrate of any of clauses 40 to 53, wherein the substrate is a die.55. A bonded substrate manufactured according to the method of any of clauses 1 to 39.

[0115] The terms “radiation” and “beam” used in relation to the lithographic apparatus encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of orabout 365, 355, 248, 193, 157 or 126 run) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0116] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0117] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description by example, and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

[0118] The breadth and scope of the present invention should not be limited by any of the abovedescribed exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A method for controlling bonding of a donor substrate to an acceptor substrate, the method comprising: treating a surface of the donor and / or acceptor substrate; and applying a substrate region specific property to the treated surface of the donor and / or acceptor substrate to locally control an evolution of a bonding wave.

2. The method of claim 1, wherein the substrate region specific property comprises any of a hydrophobicity, hydrophilicity or a chemical property.

3. The method of claim 1, wherein the step of treating the surface of the donor and / or acceptor substrate comprises forming a self-assembled monolayer on said surface.

4. The method of claim 1, wherein the step of applying a substrate region specific property comprises applying ultraviolet radiation to the donor and / or acceptor substrate.

5. The method of claim 1, wherein the step of treating the surface of the donor and / or acceptor substrate comprises forming a plurality of self-assembled monolayers on said surface and wherein at least one first self-assembled monolayer is configured to provide a hydrophobicity, hydrophilicity and / or a chemical property of said surface, and at least one second self-assembled monolayer is configured to provide a chemical affinity to a surface of a donor and / or an acceptor substrate.

6. The method of claim 1, wherein the step of treating a surface of the donor and / or acceptor substrate comprises modifying a density of dangling bonds comprised on the surface of the donor and / or acceptor substrate.

7. The method of claim 6, further comprising modifying a density of dangling bonds comprised on the surface of the donor and / or acceptor substrate by any of: applying a plasma to the surface of the donor and / or acceptor substrate; or irradiating the surface of the donor and / or acceptor substrate.

8. The method of claim 7, further comprising measuring previously manufactured examples of bonded donor and acceptor substrates to obtain bonding parameter of interest data corresponding to a bonding parameter of interest, wherein the density of dangling bonds is modified based on the bonding parameter of interest data.

9. The method of claim 8, wherein the bonding parameter of interest comprises a magnification and / or scaling overlay error component.

10. The method of claim 8, further comprising modifying the density of dangling bonds in a pattern that is the inverse of a pattern of a predicted, modelled and / or measured bonding wavefront.

11. The method of claim 1, wherein the step of treating a surface of the donor and / or acceptor substrate comprises rinsing the donor and / or acceptor substrate in a solution comprising a pH level based on an isoelectric point of the surface of the donor and / or acceptor substrate.

12. The method of claim 11, comprising: rinsing the surface of the donor and / or acceptor substrate with a solution comprising a pH level higher than the isoelectric point of the surface of the donor and / or acceptor substrate to provide a negatively charged surface, and / or; rinsing the surface of the donor and / or acceptor substrate with a solution comprising a pH level higher than the isoelectric point of the surface of the donor and / or acceptor substrate to provide a negatively charged surface, and / or rinsing the surface of the donor and / or acceptor substrate with a solution comprising a high conductivity level to provide a charge -neutral surface.

13. The method of claim 12, further comprising providing a negatively charged surface and / or positively charged surface of the donor and / or acceptor substrate to control the evolution of the bonding wave.

14. The method of claim 1, wherein the donor substrate is a die.

15. A substrate comprising a treated surface comprising a plurality of substrate regions, wherein at least one of the plurality of the substrate regions comprises a substrate region specific property configured to control the evolution of a bonding wave in a substrate-to-substrate bonding process.

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